Many biomedical implantable devices are powered from an external time varying magnetic source. The magnetic source is inductively coupled to a coil housed within the implantable device to induce an AC voltage in the coil which is then converted or rectified to a regulated DC voltage for use to power device electronics. As a general matter, higher supply voltages are often required for analog circuits, such as stimulation circuits in implantable neuro-prosthetic devices, whereas lower supply voltages are usually required for digital circuits and processors. Accordingly, a rectified or regulated DC voltage is typically maintained at a higher value for analog circuits and a linear regulator is implemented to convert the higher value DC voltage to a lower supply voltage for the digital circuits. An example of an implantable stimulator that includes both analog and digital circuitry and voltage supplies providing a range of output voltages is found in U.S. Pat. No. 6,185,452 to Schulman, et al. As has been recognized, the approach taken in the art to generate multiple supply voltages as described above, is not very power efficient especially when considering the limited power availability from weak inductive coupling of the implanted device with the external time varying magnetic source. Attempts have been made to improve power efficiency such as the use of Buck converters and switchable capacitor converters, however they may not be suitable for neuro-prosthetic and biomedical implant applications due to the limited space available within the devices which typically can only accommodate a few discrete components. Accordingly, what is needed to satisfy the shortcomings of the prior art is an approach based on a direct conversion of the induced AC voltage to a regulated DC voltage which achieves high conversion efficiency using circuitry sufficiently small to be housed in small implantable devices.